It is known that such lighting devices include a light source situated at the first focus of a reflector of the elliptical type, a convergent lens being disposed in front of the light source so that the object focus of this lens coincides with the second focus of the elliptical reflector, the first and second foci of the elliptical reflector defining an optical axis of the lighting or indicating device.
In this way, the elliptical reflector mirror forms on the light source a real image at its second focus, which is then projected by the convergent lens, usually plano-convex, onto the road in front of the vehicle. The elliptical reflector can then have a design designed so that the lighting beam thus formed corresponds to the regulations for a regulatory “main beam”.
With such a lighting or signaling device, when it is wished to produce a regulatory “dipped” lighting beam, it is known how to dispose a screen, extending in a plane perpendicular to the optical axis and situated in the focal plane of the convergent lens, the edge of this screen being disposed in the immediate vicinity of the optical axis so as to obscure some of the light rays reaching the convergent lens and thus to determine an upper cutoff in the beam emerging from the convergent lens and projected onto the road, so as not to dazzle the drivers of vehicles traveling in the opposite direction.
Also as known, the same headlight can be used for producing these two main and dipped beams selectively. It suffices in fact to make the screen movable, between a position in which it forms the cutoff of the final dipped beam by intercepting some of the light rays, and in a position in which it is away from the light beam incident on the convergent lens so as to form a main beam without cutoff.
In the case of such a headlight able to selectively emit main or dipped beams, with different photometries, by virtue of the use of a movable screen, the same reflector is used for producing these two beams. It is then necessary for the elliptical reflector to be capable of constructing a light beam with a long range for a main beam and with large width for a dipped beam. These two characteristics being contradictory, the elliptical reflector is therefore designed according to a compromise in order to be able to produce these two beams to the best possible extent.
The result is therefore that each beam, main or dipped, considered individually, although perfectly in accordance with the regulations, does not have all the characteristics of a beam constructed by a headlight dedicated to a single dipped or main beam function, in terms of visual comfort for the vehicle driver equipped with a single-beam headlight. It is therefore desirable in this case to correct at least one of the beams in order to improve its photometry.
Moreover, it is desirable to implement lighting functions which are added to those which are provided for main or dipped beams. For example, in rainy weather, it may be wished to illuminate less the side of the road on which the vehicles are traveling in the opposite direction, so that their drivers are less dazzled by the reflection of the light on the part of the roadway situated between two vehicles traveling in opposite directions.
The present invention is placed in this context and its aim is to propose a lighting device for an automobile which produces at least one of the dipped beams with a regulatory photometry, and which includes means for modifying the photometry thereof at predetermined places in the light beam.
The object of the present invention is therefore a lighting device for an automobile, having a light source situated at the first focus of a reflector of the elliptical type, a convergent lens being disposed in front of the light source so that the second focus of the elliptical reflector is contained in the object focal plane of the convergent lens, the first and second foci of the elliptical reflector defining an optical axis of the lighting device.